Refugee and migrant arrivals by sea and land into Europe this year are expected to top the one million mark next week, according to the International Organisation for Migration.

The Geneva-based agency said 990,761 people have arrived from Africa or the Middle East, with more than 800,000 crossing from Turkey to Greece alone. More than half of those - about 455,000 - were Syrians.

The IOM estimates the one million mark will be reached by Tuesday, more than four times the total of 240,000 crossings by land and sea into Europe last year.